Screw propeller



March 30, 1937'. Y F. s. WELM'AN SCREW PROPEL-LER 3 Sheets-Sheet 1 Filed April 16, 1936 March 30, 1937. F. s. WELMAN SCREW PROPELLER Filed April 16, 1936 5 Sheets-Sheet 2v March 30,1937. F W'ELMAN 2,075,682

SCREW PROPELLER Filed April 16, 1936 3 SheetsSheet 3 Patented Mar. 30, 1937 PATENT OFFICE 2,075,682 SCREW PROPELLER Francis Samuel Welman, Bexley Heath, England, assignor to C. L. W. Aviation Company, Limited, Gravesend, England, a company oi Great Britain Application April 16, 1936,

In'Great Britain March 8,

Claims.

5 along its shaft. The object of the invention is to provide a simple and robust mechanism comprising a minimum number of parts all contained within a hub structure and in which stresses involved in angular rotation of the blades for pitch 1o adjustment are substantially balanced.

pressure blocks or According to this invention the roots of the blades of a variable pitch propeller are swingable around towage points offset from the longitudinal axes of the blades and engaged with members carried by the shaft. The drive from the shaft to the blades is through the pressure blocks and offset towage points and the tractive efiort of the blades is imparted to the shaft through the towage points and pressure blocks. Thus, the torque of the propeller shaft is not transmitted directly to the propeller hub in which the roots of the blades can turn but to the said towage points. The varying direction of the air flow, due to varying conditions of flight, causes 'the roots of the blades to move around their respective towage points, the blades being thereby'turned to alter their pitch, and the said hub being free to travel along and aroundthe propeller shaft to allow of such movement of the blade roots. Thus, this automatic pitch varying mechanism comprises a very small number of parts of robust construction, all of which are enclosed by the movable box-like hub and is adapted for giving very eficient and reliable pitch variation to suit instant conditions.

The offset towage points are suitably provided by'fixing cranks to the roots of the blades. A

boss at one end of a crank is secured to the root' of a blade, and a towage pm at the other end of the crank consitutes the towage. point, this towage pin being disposed so that upon looking along the axis of the blade towards it root, the towage pin is on the windward or after side of the blade and slightly ahead of its mean centre of pressure in regard to its direction of travel. It is for this reason that the towage pins are said to form offset towing points at the roots of the blades. The effect of these offset points, as already explained, is to cause the blades to take up an appropriate angle of incidence in relation to the direction of the air flow, the blades being free to do this by reason of the movement of the hub on the shaft and the revoluble mounting of their roots. v

The pressure blocks pivotally engaged by the by the arrow A. Assuming now Serial No. 74,737 19 35 towage pins are strongly mounted on the propeller shaft. Thus, they may be supported perpendicularly to the propeller shaft by means of robust arms projecting from a collar or sleeve fixed on the propeller shaft. As themovements of the parts during pitch variation require a little flexibility in the mounting of the blocks, the inner ends of the latter may be mounted upon strong pivot pins parallel with the axis of the shaft and rigidly supported between pairs of arms on the shaft.

The box-like hub has sleeve bearings upon the shaft and these enable it to turn a-little in rela-.. tion to the shaft as demanded by the angular displacement of the blade -roots around their towage points during pitch variation.

Reference will now be madeto the accompanying drawings which include diagrams illustrating the operation of a' propeller in accordance with the invention and sectional views of one practical example of construction:-

Figure 1 is a diagrammatic plan section showing the position of the towage point and blade sections in the coarse pitch position.

Figure 2 is a view'similar to Figure blade sections in the fine pitch position.

Figure 3 is a diagrammatic rear elevation of a propeller blade mounting, with the blades adjusted to a coarse pitch position and Figure 4 is a plan of Figure 3.-

Figure 5 is a diagrammatic 'view similar to Figure 3 with the blades adjusted to a fine pitch position and Figure 6 is a plan of Figure 5.

Figure '7 is an end sectional elevation looking from the rear of part of a constructional example, showing the pitch adjusting mechanism.

Figure 8 is a plan section on the line VIII- VIII, Figure 7. s

Figure 9 is a side elevation of Figure 7, with parts in section to showthe hub mechanism and Figure 10 is a side elevation to a smaller scale of the propeller and pitch adjusting mechanism shown in Figures 7-9.

According to Figure l the bladevof a propeller is shown in the coarse pitch position. It is to be assumed now that the aeroplanes isstationary and that the propeller is revolving. In these conditions it is desirable that the blades shall be adjusted into 'a fine pitch position. In 'the'flgure the axis of the propeller shaft is represented by the line X-Y, while the directionofrevolution is indicated by the circular arrow. The direction of air flow relative to the blade is indicated that the blade is root axis into the plane represented by the line C-D. This action is counteracted by the head resistance to the air flow A offered by the root and middle sections R and M of the blade. Now,

if an aerofoilsection is hinged at its leading edge, an airflow at an appropriate angle of incidence will'liit; the aerofoil about such leading edge. Thus in the position of the blade as shown the airflow will act on the tip section T and tend to'tur'n it in the clockwise direction. As the centrifugal action is counterbalanced by the head'resistance offered by the root and middle sections, the air flow on the tip section T is thereby enabled to swing the blade around the point I into the fine pitch position seen in Figure 2.

when the aeroplane has attained flying speed the direction of air flow relative to the blade may be represented by the arrow B, Figure 2. In this case the blade will swing in an anticlockwise direction around the point I to enable it to take up an appropriate angle of incidence in relation to the altered direction of airflow. This action is caused by the reduced forward thrust of the sections R and M. which allows their resistance to overcome the centrifugal torque of the blades, and moves them back and along the shaft, into a coarser pitch, until the tip section T again opposes the anticlockwise motion, and stabilizes the blade unit at the required pitch.

It will be observed that the point I constituting the towage point around which the blade is to be swung is disposed on the windward or after side of the blade, and a little circularly in advance of the centres of pressure CP of the blade,

section. The towage point is conveniently located on the mean resultant of the aerodynamic forces acting on the blade. Thus if the line CPF represents the thrust on the blade and CP-G the torque, then the towage point is located along the line of the resultant CPH.

Such a disposition of the towage point enables pitch adjustments to be effected with a minimum of reatcion at this point.

In the constructions illustrated in Figures 3-6 the towage point aforesaid is constituted by a pin e disposed parallel to the longitudinal axis of the'blade and engaged in the free end of a pressure block I, mounted ona pivot pin g supported on flanges h rigid on the shaft and disposed parallel to the latter.

In order to permit the blades a to swing about the towage pins e the blades are mounted in a box-like hub b which is free to move around and along the shaft 0. Owing to the relative movement between the hub b and the blades which takes'place during pitch adjustment, the roots of the blades are revolubly mounted in bearings, b in the huh I). In order to swing a blade around its towage pin e a crank arm d is secured atone end to the root of the blade and at the other end to the towage pin e. a

In the position shown in Figures 3 and 4 the blades are in the coarse pitch position, the hub b having reached its rearward limit of travel along the propeller shaft '0. With the aeroplane stationary and the propeller revolving the blades 75 are automatically adjusted to tag? up 1 1;? li

' The box-like hub pitch position (Figures 5 and 6) as previously described. The-blades thus take up an appropriate angle of incidence about the towage pins. This adjustment is permitted by the hub b which not only slides forwardly along the hub from the position shown in Figure 4'to that shown in Figure 6, but also rotates around the shaft from the position shownin Figure 3' to that shown in Figure 5. As the flying speed increases and air flowconditions alter the blades are automatically caused to take up an appropriate angle of incidence in relation to the air flow so that the pitch is coarsened aspreviously described.

The extreme angular positions or limits of pitch variation of the blades are positively determined. by the ends of the hub b coming against abutments a on the shaft. The blades will be automatically adjusted to intermediate pitches according to instant conditions by movement about the towage pins e as the hub takes up the requisite intermediate positions along the shaft between these extreme positions.

Referring now to the example of construction illustrated by Flgures 7 to 10, each blade 11 is rotatably mounted in a box-like hub b by means of antifrictionthrust bearings 1' adapted easily to permit rotation in spite of the centrifugal force developed by the blades. The root of each blade is screw threaded and secured in a tubular socket i flanged at the bottom i for carrying the inner race of the bearing 7' the outer race being secured by a cover to the hub b by means of four through bolts 1'. b is provided with anti-friction bearings l to enable it to slide and rotate on the propeller .shaft 0. The root of each blade is formed with a central bore k to receive the boss 1 of crank arm d which boss is driven into the bore with a push-tight fit and so that the crank arm (1 lies fiat against the end face of the socket i, as shown in Figure 7. Each boss 1 with its crankd is axially secured in position in the root by means of two diametrically crossing locking bolts m. The ing purposes. Each crank d is formed with a towage pin e and each blade is free to take up an angle of incidence about its towage pin as previously described. The resultant angle of incidence may positions of the towage pins e and the centres of pressure of the blades. The correct positions may be decided either by calculation orexperiment, and external means q. The two covers q are fixed bosses I may be hollow for lightenbe modified by altering the relative.

for such adjustment may be provided. For example, as shown the bosses l of the cranks d may be formed with slots n through which the locking bolts m. pass. These slots enable the blades to be fixed upon the bosses l with a limited degree of circular adjustment.

The towage pin e of each gaged in the free end of a pressure block mounted on a pivot pin g parallel with the shaft axis and supported between flanges or end abutments h, of a sleeve h keyed, as shown in Figure 8, to thepropeller shaft c. As previously described, each towage pin e is conveniently located at a point upon the mean resultant of the aerodynamic forces acting on the blade. Thesepoints are advantageously at such. a distance from the roots of the blades that the cranks d, pins e, pressure blocks 1 and sleeve and flanges h h are all enclosed in the slidable box-like hub b. The forward limit 'of travel of the hub b giving the finest pitch is obtained by its abutment against a cap 0 secured to the forward end of. the proao'naeea peller shaft. The rearward limit of travel giving the coarsest pitch is obtained by the abut- 'ment of the bearing 1 against a shoulder on the shaft, as shown in Figure 9.

I claim:- 1. A variable pitch screw propeller comprising a propeller shaft; a hub movable axially and circumferentially of the propeller shaft, propeller blades having roots revolubly mounted in said 10 hub, spaced flange supports rigidly mounted on the shaft,,pivot pins extending between said supports and disposed parallel to the shaft, pressure blocks supported at one end by said pivotpins and extending laterally of the shaft, towage pins engaged by the other end of said blocks, and crank arms secured to the roots of the blades and said pins and swingable about the axes of said pins.

2. A variable pitch screw propeller comprising a propeller shaft, a hub movable axially and circumferentially of the propeller shaft, propeller blades revolubly mounted in said hub and hav-- ing root portions formed with a central bore, means for transmitting the .tractive effort of the blades to the shaft and the engine torque to the blades, comprising towage pins pivotally connected with the shaft and offset from the longitudinal axis of the blades, and a crank arm swingable aboutthe axis of each towage pin and provided with'a boss secured in the central bore of a blade. H

3. A variable pitchscrew propeller comprising propeller blades, a propeller shaft, towage pins, pressure blocks pivotally mounted at one end on the shaft and extending from the shaft and pivotally connected at the other end with said pins,

crank arms connected to the roots of the blades.

and swingable about the axes of said towage pins,

and a box-like hub provided with mountings for the'roots of the blades, movable around and along the shaft, and enclosing said pins, pressure blocks and crank arms.

4. A variable pitch propeller comprising a propeller shaft, a hub movable axially and circumferentially of the propeller shaft, blades revolubly mounted in the hub, towage elements carried by said blades offset from the axes thereof, connect ing means articulated to said towage elements 5 and to said shaft and constituting therewith a torque and thrust transmission between said shaft and blades, the articulations between said towage elements and said connectingmeans constituting centers of pitch variation of saidblades.

55 5 A variable pitch propeller comprising a propeller shaft, a hub movable axially and circumferentially of the propeller-shaft, blades revolubly mounted in the hub, towage members carried by and offset from the longitudinal axes of the bladesand connecting means articulated to said towage -members and to said shaft, said connecting means and towage members constituting drive connections between the shaft and the blades, the latter being automatically swingable around respective towage members forpitch 5 adjustment.

6. In a variable pitch screw propeller having blades automatically adjustable to appropriate angles of incidence in relation'to the direction of air flow, the combination comprising propeller 0 blades, a propeller shaft, a hub movable axially and circumferentially of the propeller shaft and having revoluble mountings for the blades, towpins carried by and offset from the longitudinal axes of the blades. and connecting means articulated to said towage pins and to said shaft, said connecting means and towage pins constituting drive connections between the shaft and the blades, each pin constituting an offset axis around which a respective blade 'is swung for pitch adjustment.

'7. In a variable pitch screw propeller having blades automatically adjustable to appropriate angles of incidence in'relation. to the direction of air flow, the combination comprising propeller blades, a propeller shaft, a hub movable axially and circumferentially of the propeller shaft and having revoluble mountings for the blades, towage pins oflfset from the longitudinal axes of the blades, connecting-means articulated to said towage pins and to said shaft, and crank connecters between the roots of the blades and said towage pins, said crank connecters and blades being swingable about'the axes of said towage pins for pitch adjustment, said towage pins, connecting means and crank connecters constituting drive connections between blades automatically angles of incidence in relation to the direction of air flow, the combination comprising propeller blades, a propeller shaft, a. hub movable axially and circumferentially of the propeller shaft and having revoluble mountings for the blades, towage pins pivotally connected with the shaft and offset from the longitudinal axis of the. blade on the pressure side thereof in advance of the mean center of pressure in regard to the direction of revolution, and crank connecters between said blades and towage pins permitting each blade to swing about a respective towage pin for pitch adjustment, said towage pins and crank connecters constituting drive connections between the shaft and the blades.

9. In a variable pitch screw propeller having blades automatically adjustable to appropriate angles of incidence in relation to the direction of air flow, the combination comprising propeller blades, a propeller shaft, a hub movable axially and circumferentially of the propeller shaft and having revoluble mountings for the blades, towage pins located on the mean resultant of the aerodynamic forces acting on the blade, means pivotally connecting the towage pins to'the shaft and crank connecters between said blades and towage pins permitting each bladeto swing about a respective towage pin forpitch adjustment, said towage pins and crank connecters constituting drive connections between the shaft and the blades. r

10. In a variable pitch screw propeller having blades automatically adjustable to appropriate angles of incidence in relation to the direction of air flow, the combination comprising propeller blades, a propeller shaft, a hub, movable axially and circumferentially of the propeller shaft and having revoluble mountings for the blades, towage pins offset from the longitudinal axis of the blades, pressure blockspivotally carried by the shaft and pivotally connected with said towage pins, and crank arms fixed to the roots of the blades and swingable about the axis of said pins the shaft and the blades. I 8. In a variable pitch screw propeller having adjustable to appropriate i for pitch adjustment, said towage piiisj-pressure blocks, and arms constituting drive connections between the shaft-and the blades.

FRANCIS SAMUEL WELMAN. 

